Psychiatrists are to discuss the merits of controversial electric shock therapy for patients suffering from a mental disorder.

A debate on electro convulsive therapy (ECT) is due to take place at the Institute of Psychiatry in London on Wednesday.

ECT involves passing an electric current through a patient's brain.

The technique is used in Britain approximately 50,000 times a year, with patients typically undergoing a course of successive treatments.

Its purpose is to improve mental conditions such as depression and schizophrenia by passing up to 400 volts through the brain.

Psychiatrists admit they don't know exactly how it works, but in provoking fits, it appears to "realign" the brain.

But many patients say the treatment - which featured in the 1975 film One Flew Over the Cuckoo's Nest - and its after-effects, are worse than their original illness.

Indeed, some patients have threatened to take legal action after undergoing the therapy.

The high-profile debate at the Maudsley Hospital in London, will provide a forum for the pros and cons of the treatment.

Dr Mark Salter, a consultant psychiatrist at St Bartholemew's Hospital in London is putting the case for the treatment.

Dr Salter, who himself has administered ECT, said: "The emotional debate obscures the arguments in favour of ECT. I am certainly in favour of ECT as a treatment of last resort.

"It's the one reliable treatment for severe psychotic depression, which can kill people."

He said that this kind of depression could result in the patient trying to take his or her own life.

He said: "There is little doubt it is a physical disorder, and ECT cures that. ECT definitely saves lives. You should see someone when they are starving and dehydrating themselves to death.

"The change after a couple of ECTs is incredible. You are saving them and their families."

But many patients and families do not agree. The 600 members of ECT Anonymous - a "survivors" group - say that their memories have been erased by the treatment, and that their physical health has been impaired.

The group was invited to join the debate, but instead decided to boycott it.

Spokesman Roy Butterfield said: "It is no good putting the case for and against, it is not as simple as that.

"Of course there are cases when ECT works, we're not denying that. What we are saying is that there are many, many cases where the side effects have been devastating, and you have to weigh up whether the risk is worth taking.

"We do not think that clinics are carrying out ECT in a safe manner, and it is pot luck whether a patient gets the correct dosage for them."

He says that half of those treated suffer "appalling side-effects" and that the NHS should prepare itself for a number of compensation claims from those who have endured it - often against their will.

The debate is to be held at the Institute of Psychiatry, De Crespigny Park, London, SE5, on Wednesday 26 January 2000, at 6pm. It is open to members of the public.